1. Technical Field
This disclosure relates to signal processing systems. In particular, this disclosure relates to a system that reduces acoustic feedback.
2. Related Art
In two-way speech communication between parties that simultaneously transmit and receive audio signals, some suppression of signals may occur. Without such signal suppression, feedback may occur, which may affect the quality and intelligibility of a voice conversation. Acoustic feedback may degrade the communication signal.
Hands-free voice communication systems in vehicles may suffer from feedback. Vehicle communication systems may allow for hands-free telephony with remote subscribers at a far end outside the vehicle, and may also allow for inter-cabin communication. Microphones and loudspeakers provided for front-seat and backseat passengers may provide improved acoustic conditions in the presence of background noise.
Methods to reduce acoustical feedback may utilize filters, similar to the echo compensation filters used in mobile telephones. Linear or nonlinear filters may synthesize a replica of the acoustic feedback, and a compensation signal may be obtained from the received signal of the loudspeakers. The compensation signal may be subtracted from the microphone output signal to generate a resulting signal.
However, it may be difficult to adapt the filter with high accuracy and an acceptable convergence rate. The impulse response may be identified for the frequencies showing the strongest feedback only, allowing in principle, adaptation of the filter coefficients for these frequencies. However, the filters may not be reliable at other frequencies. Consequently, perceptible artifacts caused by acoustic feedback may affect the intelligibility of acoustic signals. Therefore, there is a need for a system that reduces feedback.